FIG. 3 is a diagrammatic side view showing a conventional wheel mounted loader.
This wheel mounted loader 1 is a so-called articulated type wheel mounted loader and is constituted by a front frame 2 which constitutes the essential portion of the front portion of the wheel and a rear frame 3 separate from the front frame 2 and constitutes the essential portion of the rear portion of the frame. These front frame 2 and the rear frame 3 are interconnected by a center hinge pin 4 as shown in FIG. 4 taken along a line A--A in FIG. 3.
Reference numerals 4 and 5 shown in FIG. 3 respectively show the front wheel and the rear wheel of the wheel mounted type loader 1, while reference numerals 6, 7, 8 and 9 respectively show a bucket, a boom, a bucket cylinder and a boom cylinder. Reference numeral 10 shown in FIG. 4 represents steering cylinders, while 11 represents pivot pins of the steering cylinders.
The prior art front frame 2 of the wheel mounted loader 1 described above will be described in detail.
FIG. 5 is a diagrammatic perspective view showing a prior art front frame 2. The front frame 2 is constituted by a lower frame 20 constituting the lower portion of the front frame 2, and a upper frame 21 mounted on the upper portion of the lower frame 20 and formed with various bearing openings.
The lower frame 20 is constituted by a front face plate 22 covering the front surface of the front frame 2, and a pair of side plates 23 covering the side surfaces, whereas the upper frame 21 is constituted by a upper plate 24 covering the upper portion of the front frame 2, and a pair of side plates 25 which are separate from the side plates 23 and arranged on both sides of the upper portions of the side plates 23. The pair of side plates 25 are welded to the side surfaces of the side plates 23 through reinforcing ribs 26, whereby the side plates 25 are securely fastened to the side surfaces of the side plate 23.
In FIG. 5, reference numeral 30 designates a pair of boom pivots formed through the side plates 23 and 25 respectively, 31 designates a pair of boom cylinder pivot pins provided for the side plates 25, and 32 designates bucket cylinder pivots formed at the center of the upper plate 24.
With the front frame 2 described above, since the axle mounting portion 33 journalling the front wheel 4 (FIG. 3), the boom mounting portion 34 and the bucket cylinder mounting portion 35 are subjected to external force, these members are connected by welding, to the front plate 22 acting as a main reinforcing member, the side plates 23 and a center hinge 4 (FIG. 4) so as to withstand the external force. In addition, the independent side plates 25 respectively formed with boom pivots 30 and the boom cylinder pivots 31 are also connected to the side plate 23 by welding through a reinforcing rib 26. As a consequence with the construction of the prior art front frame 2, since the number of component parts and the number of welds are very large, the number of assembling steps increases, thereby decreasing the efficiency of the assembling operation and increasing the cost of manufacturing.
For the purpose of increasing the reliability and durability of the wheel mounted loader 1, it is necessary to increase the accuracy of the centers of respective pivots of the front frame 2, especially those of a pair of left and right boom pivots 30, and a pair of left and right boom cylinder pivots 31. According to the prior art construction, since the pair of left and right beam pivots 30 and the pair of boom cylinder pivots 31 described above are respectively formed on a pair of side plates 25 which are independent members. Furthermore, for the purpose of welding together, as it is necessary to position the pair of side plates 25 which have been previously formed with pivot openings before the welding operations are effected, there is a defect that the centering accuracies of respective pivots decrease due to the difficulty of ensuring the positioning accuracy of respective side plates at the time of welding as well as due to an elongation and contraction at the time of solidification of the welded metal.
In view of the problems described above, it is the object of this invention to provide a front frame of the wheel mounted type, which bears low cost and high reliability and durability by reducing the number of parts and welds of the upper frame constituting the upper portion of a front frame and by improving the center accuracy of pivot openings formed in the upper frame.